I’ll take another look at the specimen this week, and see if I can get some microscope photos of the rhizines, and I’ll update this observation. I have some collections to send to Esslinger, maybe he’ll take a look at this one for me too.

The Black Hills are most similar to the east slope of the Colorado Rockies, but there are no treatments for that region, either. Wetmore’s checklist is a fine example of thorough and insightful work, but alas, badly out-dated.

I’m not sure anyone really knows the full range of Parmelia barrenoae yet. But there are definitely specimens of P. sulcata with extremely sparsely branched rhizines. Personally, I refuse to put a confident name on a specimen until I see a branch of some sort: forked = barrenoae, squarrose = sulcata. There seems to be a good gestalt, but I don’t want to “jump the gun”! But this difference between squarrose and forked rhizines is a fundamental and reliable character for the genus as a whole, a really nice either-or character. So I’m sticking to it for now.

and P. barrenoae isn’t in there. I struggled with this specimen because I could hardly call the rhizines squarrose, although some were slightly branched, thus my description “sometimes slightly squarrose or branched”. Can you suggest a better key for Black Hills lichens? I didn’t see much online other than Wetmore’s 1965 dissertation Lichens of the Black Hills, and P. barrenoae apparently was described in 2005 in The Lichenologist, so no help there either.

Very similar to P. sulcata but the rhizines are all unbranched or occasionally forked, instead of squarrose with a bunch of minute perpendicular side-branches. (The soralia also tend to be more eroded, and the lobes therefore more bent back and loose from the substrate.) It’s very hard to diagnose confidently from photos.